1. Field of the Invention
The present invention relates to a diagnostic agent for diabetes and in particular to a diagnostic agent for diabetes which comprises glucose labelled with 13C at a specific position, or pyruvic acid labelled with 13C at least one specific position.
2. Description of the Prior Art
Test methods generally used in the primary screening in diagnosis of diabetes are urine sugar test and fasting blood sugar levels test. These tests are simple and high in specificity, but are low in sensitivity and give negative results for patients with light diabetes, so 70% or more patients are missed and these tests are considered inadequate as screening tests for diabetes (Sekikawa et al., Medical Practice 10:63, 1993). On the other hand, a glucose tolerance test used for the diagnosis of diabetes brings about side effects due to administration of a large amount of glucose, and this test requires the restraint of a subject for several hours and repeated collection of blood, and imposes heavy physical burdens on the subject, and further the procedures are troublesome, so this test is actually impossible to carry out as a screening test of diabetes. Recently, blood HbAlC and fructosamine tests, which reflect average of blood sugar levels for a certain period in the past, have been introduced as screening tests of diabetes in some facilities. Under the existing circumstances, however, even those tests are cannot be said to be adequate in sensitivity and specificity for light diabetes, and there remain the problem of a difference in measurement results among facilities.
Blood sugar level, HAlC and fructosamine tests have been used widely for diagnosis of the type of diabetes, management of outpatients with diabetes, and evaluation of therapeutic effects. However, blood sugar levels would drop at the time of fasting in the case of light diabetes, while besides the above-described problems, the HAlC and fructosamine tests have the problem that the results of the tests cannot be known until a next visit to the hospital, so instructions would be given to the patient on the basis of the past test results.
Under such circumstances, there is demand for developments in a test method which is effective for patients even with light diabetes and non-invasive to the subjects and which give results immediately and accurately for diagnosis of diabetes, management of patients with diabetes and evaluation of therapeutic effects.
On the one hand, it is generally carried out to administer 13C-labeled glucose and measure 13C exhausting as carbon dioxide into an exhalation in order to assess energy expenditure. Because this analysis should be conducted under steady state, glucose should be administered for a long period before examination [J. J. Robert et al., J. Appl. Physiol. 63, 1725-1732 (1987)]. Therefore, this analysis requires a long period for examination and imposes the heavy pains on the subject, and is thus practically not usable for diagnosis of diabetes.
It is reported that after naturally labelled 13C-glucose prepared from C4 plants is bolus administered, the degree of exhalation of 13CO2 is reduced in the case of patients with diabetes [P. Lefebvre, et al., Diaetologia 14, 39-45 (1978); M. J. Arnaud, et al., Nutrition and the Diabetic Child, Pediat. Adolesc. Endocr. vol. 7, pp. 203-212, 1979]. However, because naturally labelled 13C-glucose have 6 carbons randomly labeled, we can scarcely evaluate an alternation of the metabolic pathway of glucose. Further, because the concentration of 13C in naturally labelled 13C-glucose is 2% or thereabout, it is necessary to administer a large amount of glucose in order to monitor a change in the concentration of CO2 in an exhalation, and the burdens on the subject are therefore heavy.
The object of the present invention is to provide a diagnostic agent for diabetes to give accurate results immediately with few pains on the subject.
As a result of their eager research, the present inventors found that diabetes and its type can be accurately diagnosed by administering glucose labelled with 13C at a specific position or pyruvic acid labelled with 13C at least one specific position, and then determining degrees of increase of 13C levels in exhaled CO2, and they thereby arrived at the completion of the present invention.
That is, the present invention relates to a diagnostic agent for diabetes comprising glucose labelled with 13C at a specific position.
The present invention further relates to a diagnostic agent for diabetes comprising pyruvic acid labelled with 13C at least one specific position.